The present invention relates to the deflection yoke for use in the color cathode-ray tube which provides three electron beams in an in-line arrangement.
As known, the color cathode-ray tube provided with the electron guns which emit three electron beams in the in-line arrangement employs the deflection yoke which ensures normal convergence of three electron beams only by the deflection magnetic field of the deflection yoke. Such deflection yoke makes the magnetic field produced by the horizontal deflection coil a pincushion-distributed magnetic field and the magnetic field produced by the vertical deflection coil a barrel-distributed magnetic field to carry out convergence correction and this deflection yoke is therefore referred to as the self-convergence type deflection yoke.
A pincushion distortion resulting from the barrel-distributed magnetic field at the screen side of the vertical deflection magnetic field produced from the vertical deflection coil takes place at the right and left ends of the picture on the fluorescent screen of the color cathode-ray tube in addition to the pincushion distortion resulting from the curvature of the fluorescent screen of the cathode-ray tube.
Conventionally, the pincushion distortion, so-called "side pincushion distortion" which takes place at the right and left ends of the picture as described above is corrected by means of a special pincushion distortion correction circuit or by forming the vertical deflection magnetic field of the deflection yoke in the shape of pincushion at the screen side, that is, the front side of the deflection yoke and in the shape of barrel at the electron gun side, that is, the rear side of the deflection yoke, without using the pincushion distortion correction circuit.
Such deflection yoke which is referred to as the side pincushionless type deflection yoke includes (1) the deflection yoke comprising the vertical deflection coil which is wound to generate a pincushion-distributed magnetic field at the screen side and a barrel-distributed vertical deflection magnetic field of the vertical deflection coil at the electron gun side, (2) the deflection yoke provided with a set of magnetic plates as described in the U.K. patent publication No. GB 2010005A and (3) the deflection yoke for wide angle deflection which is made up by combining the deflection yokes described in (1) and (2).
In case of the deflection yoke as described above, however, the misconvergence of the vertical deflection magnetic field produced by the vertical deflection coil cannot be corrected only by virtue of the increased intensity of the barrel-distributed magnetic field at the electron gun side. For example, a horizontal misconvergence that the raster B formed by the blue beam 22 at the corners of the picture is not converged to the raster R formed by the red beam 24 takes place as shown in FIG. 1 and, for example, a vertical misconvergence takes place as shown in FIG. 2 when the deflection sensitivity for the green beam 23 which forms the raster G at the corners of the picture is insufficient and it is consequently difficult to obtain high quality pictures on the screen.